Production of light-sensitive diazotype materials



March 1952 R. J. KLIMKOWSKI ETAL 3,02

PRODUCTION OF LIGHT-SENSITIVE DIAZOTYPE MATERIALS Filed NOV. 22, 1957 FIGI omzo LAYER 2 -17 KCONTAINING THFA PAPER PRECOAT LAYER CONTAINING SILICA AND/OR RESIN AND THFA FIG?) rm n on: omzo LAYER E INVENTORS:

ROBERT J. KLIMKOWSEKI ERNEST A. KAHN BY w ywad 1%.;

ATT'YS United States Patent @ffice 3,027,256 Patented Mar. 27, 1962 3,027,256 PRQDUTION F LIGHT-SENSITIVE DIAZOTYPE MATERIALS Robert J. Klimlrowslri and Ernest A. Kahn, Chicago, Ill.,

assignors to Eugene Dietzgen Co., Chicago, 11]., a corporation of Delaware Filed Nov. 22, 1957, Ser. No. 698,149 3 Claims. (Cl. 96-49) This invention relates to the production of light-sensitive diazotype materials, and to new methods, compositions and materials. More particularly, the invention relates to an improvement for increasing the developing speed of exposed diazotype materials and for improving the intensity or density of the resulting developed print.

The diazotype reproduction processes are based on light-sensitive diazo compounds coated on a suitable base, and a colored, positive azo dye image is formed on the base fro-m a positive master. Exposure to ultraviolet light under a translucent master or original, such as an engineering drawing, type material or other design, Will decompose the diazo compound Where it has been struck by light, and retain the diazo compound where it has been protected from light by the opaque areas of the original. The print is then developed by reacting the retained diazo compound with a coupler, to form a highly colored azo dyestuff, in precise duplication of the original.

The diazotype reproduction processes are divided into two categories, the moist process and the dry process. The moist process is a one-component diazotype process in which the diazo is on the base while the coupler is applied to the coated surface in a developer solution. The dry process is a two-component process in which both the diazo and the coupler are on the base and in which development is achieved without Wetting, such as through the use of moist ammonia vapors to induce the coupling reaction. The present invention is concerned with improvements in the dry process, and particularly, in the manufacture and use of the diazotype materials.

Modern diazotype processing equipment is constructed in a manner to allow the print to be developed at the same speed as the printing is accomplished. It is customary in the dry process to effect the exposure and development in one and the same machine containing an ammonia developing chamber. High production rates are desired, employing high speed equipment and utilizing strong lights of high actinic efiiciency, thus printing the materials at rapid rates. It is then necesary to develop the prints at the same rapid rates. With such high speed developing, it has been found necessary to accelerate the normal rate of ammonia development.

In order to accelerate development of the prints at various printing speeds, present commercial practice involves the provision in or at the light-sensitive layer of a humectant or hygroscopic material to assist in absorbing the moist ammonia vapors, such as a polyhydric alco- 1101, for example, glycerine, ethylene glycol or diethylene glycol, or zinc chloride. However, the quantity of hygroscopic material must be carefully chosen, as too large an amount will cause the print to have an objection-able sticky, limp feel. An insufficient amount of humectant causes the print to develop only slowly and often incompletely. The humectant is generally detrimental to shelf life. Even when the amount of humectant is carefully chosen, its use is an unsatisfactory solution to the prob lem of development rate. Changes in temperature, humidity, and rate of travel through the developer part of the diazotype processor are variables for which the addition of the humectant does not compensate.

It has previously been proposed to alleviate these difficulties by methods which are, however, limited in their application. Oarboxamides have been provided in the light-sensitive layer, and thiourea derivatives have been provided in the light-sensitive layer.

It has now been discovered in the invention that the development of a dry process or dry-developing lightsensitive diazotype composition is markedly improved when conducted in the presence of tetrahydrofurfuryl alcohol (also referred to herein as THFA). The development rate is substantially increased, and prints of markedly increased density or depth of color are produced. Whereas chemical agents which accelerate ammonia development of diazotype materials frequently accelerate the deterioration of the sensitized product upon storage, the provision of THFA in the diaztoype materials does not detract from the shelf life.

The invention provides a new and improved process for producing prints from a light-sensitive diazotype material, methods for manufacturing an improved diazotype material, compositions adapted for the manufacture of the materials, and improved base materials and diazotype printing materials.

Various procedures are contemplated for developing the prints in the presence of THFA to provide the foregoing and other advantages. The lightsonsitive diazotype layer is contacted with T l-EPA, and the layer is contacted with preferably ammonia vapor. The THFA is preferably incorporated in a supported layer of a dry process light-sensitive diazo composition. This is preferably done by applying a suitable two-component diazotype composition, which may be a conventional composition, to a conventional base together with the THFA. The THFA may also be applied to a base before or after the diazo composition, in a manner which provides contact thereof with the di'azo layer. Thus, THFA may be applied in a precoat. The THFA might be applied after the diazo layer is formed, however, this method is not preferred because the THFA may cause some leaching of organic compounds from the layer.

In the preferred method, a solution of a conventional dry process light-sensitive diazotype composition also containing THFA is applied in the conventional manner to a base, and the coated base is dried, also in conventional manner. It is preferred to employ an aqueous solution of the diazo compound, coupler and adjuncts which also contains about 1% to 20% of THFA, by volume, based upon the volume of water in the sensitizing solution. It is further preferred that the volume proportion of THFA be about 2% to 10% for best results. Above about 10%, there may be some diminishment of the desired smooth appearance. In the process of sensitizing a base, the wet-coated base is dried to remove volatiles. Water and any organic solvent is evaporated, and also, a quantity of the THFA and part of the volatile humectant evaporates. Employing the conventional coating compositions and proportions Wtih the foregoing quantities of THFA, and with the conventional drying methods, effective quantities of THFA and the humectant remain.

The sensitizing solution may contain the humectant, such as one of those previously described, in the conventional or in a reduced amount. It is a feature of the present invention that a humectant may be dispensed with entirely, to eliminate its effect on shelf life. In this connection, it is interesting to note that THFA is apparently not hygroscopic. In ordinary use, however, it is advantageous to include a quantity of one of the conventional humectants, as it contributes to rapid development. Thus, it is preferred that one of the: above humectants be present in a volume ratio, humectantzTHFA, of about 2:1 to 6:1. The preferred humectant is ethylene glycol. The ratio may vary beyond these limits when different humectants are employed and depending upon manufacturing conditions.

The invention provides an improved rate of development for the diazoty-pe materials characterized as fast and extra fast, and it provides improved print or image density for these papers and for the slow and standard materials where development rate is not so important. The diazotype papers having the several printing speeds referred to may be approximately characterized by the amounts of light energy required to completely decompose the diazo compound present on the paper, in terms of watt seconds per square centimeter at a wave length of 3660 Angstroms, as follows: slow, 0.150; standard, 0.100; fast, 0.050; extra fast, 0.025.

The light-sensitive diazo compound, the azo coupling component and the other adjuncts are not critical factors in the practice of the invention. Any diazo compound and coupler suitable for producing dry process diazotype materials may be used. Exemplary diazo compounds are the diazonium salts obtained by diazotization of the following amines:

p-Amino-N,N-dimethylaniline -Amino N,N-diethylaniline p-Amino-N-ethylaniline p-Amino-N-ethyl-N-fi hydroxyethylaniline p-Amino-N-methyl-N-fl hydroxyethylaniline p-Amino-N,N-di-B hydroxyethylaniline p-Amino-m-ethoxy-N,N-diethylaniline p-Amino-N-ethyl-o-toluidine p-Amino-N-ethyl-m-toluidine p-Amino-N,N-diethyl-m-toluidine p-Amino-N-ethyl-N-benzylaniline .p-Amino-N-ethyl-N-.;8 hydroxyethyLm-toluidine N-p-amino-phenylrnorpholine p-Amino-diphenylamine 3-aminocarbazole And the like.

These diazonium salts are commonly employed as their stabilized double salts, e.g., their zinc chloride, cadmium chloride, or stannic chloride double salts.

Exemplary suitable azo coupling components are the following:

2,S-dihydroxynaphthalene 2,3-dihydroxynaphth-alene-6-sulfonic acid Resorcinol Phloroglucinol Acetoacetanilide 7-hydroxy-1,2-naphthimidazole 1-phenyl-3-methyl-5-pyrazolone 2-naphthol-3,6-disulfonic acid And the like.

Similarly, the various adjuncts usual in the manufacture of light-sensitive diazotype materials may be employed in the sensitizing and coupling compositions, such as metal salts for intensification of the image, stabilizing agents, acids acting to retard precoupling, and others.

The various bases or supports commonly used for the production of diazotype printing materials may be employed, such as paper, resinous and resin-impregnated materials, cloth, metal, and porous materials. The sensitizing solution containing THFA is applied to a moving web, in the case of paper or sheet material, by means of an applicator roller. The excess is doctored otf by an air knife or a glass bar, and the web is dried in a chamber supplied with heated air. Other conventional methods of application might be used, such as brush coating or spraying.

It is often advantageous to apply a precoat to the base, in a manner well known to the art. Thus, finely divided silica precoats or resinous precoats, or a combination of both, are commonly applied to the base followed by application of the sensitizer. Likewise, it is often advantageous to provide a precoat when producing diazotype material according to the invention. In such case, the THFA may be applied to the base either with the precoat or with the sensitizer composition, preferably the latter.

In precoating a base such as paper with silica, an aqueous dispersion of finely divided silica is applied and the coated product is dried. The known compositions and proportions are suitable. Colloidal silica is preferred, having a particle size of about 0.1 micron or below. The particle size may, however, range up to 10 microns. Aqueous finely divided silica dispersions may be prepared in known manner from a silica powder, and the dispersion may contain an agent to stabilize the colloidal suspension. Also, one of the various commercially available preparation of aqueous finely divided silica may be employed, including available materials ranging in particle size from 0.007 to 0.1 micron and greater.

In precoating with a resinous or like material, those materials and proportions may be used which are commonly employed in the production of diazotype materials. The hydrophobic natural and synthetic resins are preferred, such as rosin derivatives, and substantially water-insoluble film-forming synthetic resins. The resins should form a clear, colorless, waterand abrasion-resistant film.

The preferred resins are hydrophobic synthetic filmforming thermoplastic addition polymers of at least one monoolefinic monomer having a polymerizable group, such as the polystyrene resins, the poly-acrylic resins and the polyvinyl resins. The polystyrene resins include, for example, homoand copolymers of styrene, and ring and side chain-substituted styrene, substituted with halo, alkyl or aryl radicals. Thus, the polymers may be prepared from vinyl toluene, alpha and betachloro and bromo styrene or alpha and beta-methyl and ethyl styrene. The polyacrylic resins include the preferred polymers of acrylic esters, such as methyl and ethyl methacrylate, and methyl and ethyl acrylate. The polyvinyl resins include the vinyl esters such as vinyl acetate, the vinyl halides such as vinyl chloride, and the vinylidene halides. Especially preferred are the butadiene-styrene copolymers and polyvinyl acetate. The polyacrylates and polystyrene are also very useful.

Resins are preferably employed finely dispersed or emulsified in an aqueous coating composition for application to a base. In this form, they are generally be-- lieved to be in or near the colloidal particle size range, e.g., about 0.2 micron or below. About 1 or 2 percent of an emulsifier may be employed to aid in forming a stable emulsion of the resin particles, in known manner. One or more resins may be provided in the coating composition and resulting layer.

A preferred coating composition is composed of both finely divided silica and a dispersed resinous material, which are intimately mixed, applied to the base and dried. The precoating composition preferably contains a concentration of about 15 to 35%, preferably about 20 to 30%, by weight of silica, and about 5 to 25%, preferably about 10 to 15% by weight of resin. The .silica and the resinous material are preferably present in a weight ratio of about 0.5 :1 to 10:1, and it is further preferred that the ratio be about 2:1 to 4:1.

When the THFA is applied to the base with the precoat, it is applied in approximately the same proportion as given above for the sensitizer, i.e., about 1% to 20% by volume of the water in the precoat composition, preferably 2% to 10%. The precoat composition is applied in the same manner as the sensitizing solution.

in the several methods of application of THFA to a base, the T HFA will be incorporated in the light-sensitive layer due to the manner of application or due to the mutual penetration or intermixing of the precoal layer and the light-sensitive layer when the THFA is applied with the precoat.

Several of the materials with which the invention is concerned are schematically illustrated in the attached drawings, each of which is an enlarged fragmentary crosssection of coated paper. In FIGURE 1, a sheet of paper 1 is illustrated as provided with a dried coat or layer 2 of a dry process light-sensitive diazotype composition also containing THFA. It will be understood that, as is usually the case, the sensitizer layer 2 penetrates the sheet of paper 1 to some extent.

FIGURE 2 illustrates a sheet of paper 1 containing a dried precoat layer 3 of silica and/or resin also containing THFA.

FIGURE 3 illustrates a sheet of paper 1 having a precoat layer 3 adjacent to the paper and a sensitizer layer 2 on the precoat layer. Again, the layers extend into each and into the paper to a certain extent. THFA is incorporated in the precoat layer 3, the sensitizer layer 2, or both.

The following examples illustrate the methods and materials of the invention. It will be understood that the invention is not limited to the examples nor to the components, proportions, conditions and procedures set forth therein.

Example I The following is a representative finely divided silica precoat composition:

Water l Magnesium aluminum silicate (Veegum) g 25 Colloidal silica, 0015-0020 micron (Cab-O- Sil) g 200 The precoat may be applied prior to a sensitizing composition containing THFA, or THFA may be included in the precoat. A preferred composition additionally contains 500 ml. of THFA, or 5% on the volume of the water.

Example 2 An exemplary silica-resin precoat composition to which up to of THFA, on the volume of the water, may be added, is as follows:

Water l 10 Magnesium aluminum silicate (Veegum) g 50 Colloidal silica, 0.1 micron, aqueous 30% solids,

(Mertone VB-4) l 3.5 Polyvinylacetate emulsion, 55% solids (Xyno Resin Example 3 The following sensitizing solution was applied to a 100% sulfite paper stock of medium Weight, which had been precoated with the composition of Example 1, containing no THFA, and dried. The solution contained 3.75% of THFA and of ethylene glycol, based on the volume of water.

The paper was dried. The resulting sensitized paper exhibited faster development characteristics, and resulted in brilliant blueline prints of greater density, than a paper sensitized with a solution of the same formulation, excepting that this control solution did not contain THFA.

Example 4 A diazo paper stock of rag content and medium 6 weight was sensitized by applying the following solution containing 2.5% of THFA and 18% of glycol, on a commercial diazotype sensitizing machine:

Water l 10 Ethylene glycol ml 1800 THFA ml. 250 Citric acid g 500 Zinc chloride g 325 Thiourea g 425 Resorcinol g 50 Phloroglucinol g 2.5 23% acetoacetanilide-77% thiourea g 12.5 2,3-dihydroxynaphthalene-6-sodium sulfonate g 200 p-Diazo- I,N-diethylaniline-zinc chloride salt g Saponin g 25 The resulting sensitized paper, after being printed under a positive master and developed, gave a blackline print of a more neutral and more intense shade, which also developed faster, than a paper sensitized with a solution of the same composition, except that the THFA had been omitted.

Example 5 A 14 lb. basis weight 100% rag raw stock paper was permanently transparentized with hydroabiethylalcohol and was then precoated with the colloidal silica-resin composition of Example 2, containing no THFA, in order to give the sensitizing solution greater adherence to the transparentized sheet. A sensitizing solution containing 4% THFA and 9% glycol, and having the following composition was applied to the dried precoated paper:

Water l 10 Ethylene glycol ml 900 THFA ml 400 Citric acid g 500 Boric acid g 250 Zinc chloride g 900 Thiourea g 600 Resorcinol g p-Diazo-N-methyl-N-hydroxyethylaniline zinc chloride double salt g 550 Saponin g 30 The sensitized paper obtained in this manner resulted in sepia line prints of excellent actinic opacity, which developed more rapidly than a paper which had been obtained by using the same formulations, excepting that the THFA had been omitted.

Example 6 The following sensitizing formulation is used to obtain rapidly developing black shades:

Example 7 A comparison was made between (1) paper precoated and sensitized according to Example 3 but containing no THFA, and (2) paper sensitized according to Example 3 with the sensitizing composition containing THFA, but not precoated. The development speed and the density of the latter paper were as good as the .former paper. Consequently, the invention enables the production of a paper comparable to prior papers without the additional expense of precoating, which previously served to increase the development speed and image density.

Example 8 A comparison was made between paper (1) of Example 7 and (3) a precoated paper prepared like paper (2) of Example 7, except that the ethylene glycol was reduced by one-half and the THFA was increased to 4.25% by volume of the water. The development rate of (3) was improved over (1) and the densities were about equal. The result was a paper with a higher development rate and a lower glycol content, which is additionally advantageous in that high glycol content contributes to poor shelf life.

Example 9 Paper (1) of Example 7 was compared with (4) a precoated paper prepared as in Example 3 except that ethylene glycol was eliminated from the sensitizing solution and 10% of THFA was provided, on the volume of the water. The development rate of (4) was improved over that of (1), although the density of (4) was slightly poorer. The paper Was characterized by exceptional development properties for a paper which contained no ethylene glycol or the like.

The foregoing comparison was repeated with paper (1) and a paper (5) which difiered from paper (4) in that it was prepared with a sensitizing solution containing twice as much THFA, or 20% on the volume of the water. The development rate of (5) was greatly improved over that of (l), and the density of (5) was also better. Furthermore, the ethylene glycol was eliminated.

Example Paper was precoated with the following composition:

Water l Magnesium aluminum silicate (Veegum) g 50 Colloidal silica (Cab-O-Sil) g 400 THFA ml 1000 The driedprecoated paper was then sensitized with the following composition:

Water 40-45 C 1 20 Ethylene glycol rnl 1000 Citric acid g 900 Zinc chloride g 1300 Thiourea g 1000 2,3-dihydroxynaphthalene-6-sodium sulfonate g 760 p-Diazo-N-ethyl-N-hydroxyethylaniline zinc chloride double salt g 240 Saponin g The foregoing paper (6) was compared with a paper (7) precoated and sensitized in the same manner except that the precoat contained no THFA. The development rate and density of paper (6) were improved over paper (7) containing no THFA in the precoat.

When paper (6.) was compared with a paper (8) which was prepared in the same manner except that the THFA was omitted from the precoat and 1000 ml., or 5% by volume, of THFA was included in the sensitizing composition, the development rate and density of (8) were improved over (6). This indicated that it is preferable to provide the THFA in the sensitizer, compared with its provision in the precoat.

When a paper (9) was precoated with the composition containing THFA as in (6 and sensitized with the sensitizer containing THFA as in 8), development rate and density were improved over materials containing no THFA. There appeared to be no advantage in providing such quantities in both the precoat and in the sensitizer coat, as compared to paper (8) containing THFA only in the sensitizer coat.

The invention thus provides new methods, compositions and materials furnishing improved results in the production of diazotype prints. The invention is especially advantageous with the fast speed printing papers, substantially increasing the development rate. The image densities are also considerably improved. The invention is characterized by its simplicity and reliability, and the improved results are not obtained at the expense of other desired properties, such as shelf life.

The-invention ishereby claimed as follows:

1. The process of producing a positive print which comprises coating the surface of a base with an aqueous solution containing p-diazo-N,N-dimethylaniline zinc chloride double salt, 2,3-dihydroxynaphthalene-6-sodium sulfonate, and about 1% to 20% of tetrahydrofurfuryl alcohol based on the volume of water in said solution, drying the coated base, exposing the coated surface to light under a design, and developing the print by contacting the exposed coated surface with ammonia vapor.

2. An improved light-sensitive diazotype material comprising a base having a dried coat of an aqueous solution containing p-diazo-N,N-dimethylaniline zinc chloride double salt, 2,S-dihydroxynaphthalene-6-sodium sulfonate, and about 1% to 20% of tetrahydrofurfuryl alcohol based on the volume of water in said solution.

3. A process for producing a positive print which comprises applying to the surface of a base an aqueous solution containing a light-sensitive stable diazonium double salt, an azo coupling compound, and from about 1% to about 20% of tetrahydrofurfuryl alcohol by volume based on the volume of water in the solution; drying the wetcoated base to remove volatiles; exposing said light-sensitive material to light under a design; and thereafter developing-the print by contacting the coated base with ammonia vapor.

References Cited in the file of this patent UNITED STATES PATENTS 2,531,485 Von Glahn et al Nov. 28, 1950 2,551,133 Jennings May 1, 1951 2,623,821 Isherwood et a1 Dec. 30, 1952 2,662,013 Sulick et al. Dec. 8, 1953 2,662,066 Clark ct al. Dec. 8, 1953. 2,826,501 Hodgins Mar. 11, 1958 OTHER REFERENCES Condensed Chemical Dictionary, V edition, 1956, Rheinhold Publishing Co., NewYork, pages 979 and 1078. 

3. A PROCESS FOR PRODUCING A POSITIVE PRINT WHICH COMPRISES APPLYING TO THE SURFACE OF A BASE AN AQUEOUS SOLUTION CONTAINING A LIGHT-SENSITIVE STABLE DIAZONIUM DOUBLE SALT, AN AZO COUPLING COMPOUND, AND FROM ABOUT 1% TO ABOUT 20% OF TETRAHYDROFURFURYL ALCOHOL BY VOLUME BASED ON THE VOLUME OF WATER IN THE SOLUTION; DRYING THE WETCOATED BASE TO REMOVE VOLATILES; EXPOSING SAID LIGHT-SENSITIVE MATERIAL TO LIGHT UNDER A DESIGN; AND THEREAFTER DEVELOPING THE PRINT BY CONTACTING THE COATED BASE WITH AMMONIA VAPOR. 